Polylactones, 39. Zn lactate-catalyzed copolymerization of L-lactide with glycolide orε-caprolactone

Abstract

Copolymerizations of glycolide (Glyc) and L-lactide (L-Lac) were conducted at 150°C in bulk to prepare random copolyesters. Four resorbable catalysts were used and compared: ZnCI 2 , ZnO 2 , Zn stearate (ZnSte 2 ) and Zn lactate (ZnLac 2 ). Separate time-conversion curves were recorded for glycolide and lactide by means of 1 H NMR spectroscopy. Glycolide polymerized faster than L-lactide under all circumstances, but the difference was smallest when ZnLac 2 was used as catalyst. Sequence analyses were performed using 13 C NMR spectroscopy. Completely random sequences were never obtained, but the sequences resulting from a catalysis with ZnLac 2 came closest to the desired randomness. Preparative 1:1 (mole ratio) polymerizations were conducted with ZnSte 2 and ZnLac 2 . High yields were obtained with both catalysts, but ZnLac 2 yielded far higher molecular weights. Furthermore, ZnLac 2 -catalyzed copolymerizations were conducted with variation of the Glyc/Lac ratio. It was found that small scale and large scale copolymerizations yield copolyesters having different properties, because the superheating in the early stage of the polymerizations (resulting from glycolide) favors the transesterification. Finally, 1:1 copolymerization of e-caprolactone and L-lactide were studied in bulk at 150°C. Again high yields, high molecular weights and nearly random sequences were obtained.